The first batch of Constitution Light Cruisers built by the Federation used tried and true laser weaponry as phasers remained in their infancy. Likewise, photon torpedo technology had not yet been successfully reverse engineered. Federation ships instead used the long range accelerator cannon to meet their needs in this area.

After the development of phaser technology, the Constitution Light Cruisers received upgrades to this new weapons technology. This was a priority for Starfleet and was done relatively quickly.

Based on the failed Star Trek pilot "The Cage" and other statements made throughout the series, it can be determined that the Federation used laser weapons during the early missions of the U.S.S. Enterprise which were later replaced with new phaser weapony. This ship is meant to represent this pre-phaser model of the Constitution.